In an imaging device such as a camera, an optical diaphragm device is used for adjusting an amount of light from an imaging object which is incident on an imaging plane. The optical diaphragm device includes a circular ring-like housing body. When an aperture diameter of a diaphragm aperture becomes maximum (fully open), a diaphragm blade is retracted within a width of the housing body. Accordingly, with respect to a width of the housing body, it is necessary to ensure at least a width equal to or more than a width of the diaphragm blade as a retraction space for the diaphragm blade.
To narrow such a retraction space for the diaphragm blade for realizing downsizing of the optical diaphragm device, there has been conventionally made an attempt to narrow a width per se of the diaphragm blade (narrowing of a width of the diaphragm blade).
However, it is also known that when narrowing of the width of the diaphragm blade progresses, there arises a drawback that light easily leaks at a portion other than the diaphragm aperture.
To overcome such a drawback on leakage of light, there has been conventionally known an optical diaphragm device where a light leakage prevention blade is introduced in addition to a diaphragm blade, and a gap which causes leakage of light is shielded by the light leakage prevention blade (see patent literature 1, for example).
FIG. 8A to FIG. 8D are plan views for describing a conventional optical diaphragm device 900. FIG. 8A is a plan view of the optical diaphragm device 900 as viewed in a plan view along an optical axis OA. In FIG. 8A, only a state where light leakage prevention blades 920 protrude is shown, and the illustration of diaphragm blades 910 is omitted. FIG. 8B is a plan view showing the diaphragm blade 910, and FIG. 8C is a plan view showing the light leakage prevention blade 920, and FIG. 8D is a plan view showing a housing body 940.
As shown in FIG. 8A to FIG. 8D, the conventional optical diaphragm device 900 is an optical diaphragm device 900 for changing an aperture diameter of a diaphragm aperture by advancing or retracting a plurality of blades to and from the optical axis OA. The optical diaphragm device 900 includes: a plurality of diaphragm blades 910 each having a diaphragm blade body 911, a diaphragm blade fixing boss 912 protruding from one surface of the diaphragm blade body 911 toward a side in a first direction along the optical axis OA, and a diaphragm blade moving boss 913 protruding from the other surface of the diaphragm blade body 911 toward a side in a second direction opposite to the first direction; a plurality of light leakage prevention blades 920 each forming a pair with each of the above-mentioned diaphragm blades 910, each light leakage prevention blade 920 having a light leakage prevention blade body 921, a light leakage prevention blade fixing boss 922 protruding from one surface of the light leakage prevention blade body 921 toward the side in the first direction, and a light leakage prevention blade moving boss 923 protruding from the other surface of the light leakage prevention blade body 921 toward the side in the second direction; a drive ring 930 having cam grooves 933 in each of which the moving boss is inserted in a state where a distance between the cam groove 933 and the optical axis OA differs corresponding to a position of the groove, the drive ring 930 being capable of rotating about the optical axis OA so as to move the cam grooves 933 in a circumferential direction about the optical axis OA; and a housing body 940 housing the diaphragm blades 910, the light leakage prevention blades 920, and the drive rig 930. The optical diaphragm device 900 includes a plurality of pairs each consisting of the diaphragm blade 910 and the light leakage prevention blade 920 (six pairs in the conventional optical diaphragm device 900 shown in FIG. 8A to FIG. 8D). The cam grooves 933 are formed in the drive ring 930. The number of cam grooves 930 corresponds to the number of pairs each consisting of the diaphragm blade 910 and the light leakage prevention blade 920. A plurality of pairs each consisting of a first hole 941j and a second hole 942j are formed in the housing body 940 corresponding to the plurality of pairs each consisting of the diaphragm blade 910 and the light leakage prevention blade 920. The diaphragm blade fixing boss 912 and the light leakage prevention blade fixing boss 922 are inserted into the pair of the first hole 941j and the second hole 942j respectively. The number of pairs each consisting of the first hole 941j and the second hole 942j corresponds to the number of pairs each consisting of the diaphragm blade and the light leakage prevention blade. With respect to the diaphragm blade 910 and the light leakage prevention blade 920 which form the stacked pair, the diaphragm blade moving boss 913 and the light leakage prevention blade moving boss 923 are respectively inserted into one cam groove 933 (j: an integer of 1 or more).
According to the conventional optical diaphragm device 900, the light leakage prevention blades 920 can be added while using the existing basic structure for driving the diaphragm blades (the housing body, the drive ring and the like) without modification and hence, leakage of light brought about by narrowing of a width of the diaphragm blade can be prevented.